Because of documented contamination of a large area of land with plutonium and other transuranic radionuclides in the vicinity of the Rocky Flats nuclear weapons plant in the Denver Standard Metropolitan Statistical Area (S.M.S.A.) there is community concern regarding possible health effects in populations living in this area as well as concern for the safety of a further residential developoment near the plant. A preliminary study of age-corrected cancer death rates in eight contaminated census tracts around the plant compared with a control area of 19 census tracts with a similar population in a relatively uncontaminated part of the S.M.S.A. disclosed a significant increase in deaths from leukemia and lung cancer in the contaminated area. The study has been expanded to evaluate in census tract areas selected by concentrations of plutonium in soil or in surface respirable dust. The first phase of the study is the evaluation of cancer incidence in the contaminated and the uncontamianted census tract areas of the S.M.S.A., utilizing data from the Third National Cancer Incidence Survey of 1969-71 by the National cancer Institute. Cancer incidence in the contaminated areas, corrected for age, sex, race, ethnicity, income and education, will be compared to that in the uncontaminated census tract area of the S.M.S.A. by several methods, including regression analysis. The second phase is the evaluation of cancer death rates between 1970 and 1980, and the third phase will be an analysis of cancer incidence in the period 1979-81, using the same study and control areas as in the first phase. Cancer death and incidence data will be supplied by the Colorado Health Department, Division of Vital Statistics and the Colorado Cancer registry. The effect of exposure to small concentrations of plutonium and other transuranics on a general population living in a contaminated area has never yet been evaluated with this epidemiologic approach, and the results will be of considerable value in selecting sites for plutonium processing plants and nuclear-electric generating plants in relation to population centers. These investigations will be followed by a prospective study extending to 1981 (Phase four).